a. Field of the Invention
This invention relates to a commutator. More particularly, it is concerned with a method for readily mass-producing a commutator having predetermined electrical characteristics (such as contact resistance, contact ripper, etc.), mechanical characteristics (such as low friction, low brush noise, etc.), and high mechanical strength as required of it so as to be adaptable to particular rotary machines.
b. Description of Prior Arts
Heretofore, this kind of commutator has been manufactured by punching sheet metal material, using a pressing machine, in a predetermined shape of the commutator having required numbers divided commutator segments, and the thus punch-shaped metal sheets are laminated in a plurality of numbers to a predetermined thickness.
According to such method of manufacture, however, since the sheet metal should be formed in a predetermined cross-sectional shape of the commutator segments by the punching press, then the metal sheet thus punch-shaped should further be laminated to a predetermined thickness to obtain a desired commutator, and other process steps should be taken up, maintenance in precision of the size is difficult, and, in particular, when the commutator for a small or miniature-sized motor is to be manufactured, it is all the more difficult to form such mini-size cross-sectional pattern of the commutator segments by the punching press, on account of which productivity of the commutator cannot but be low inevitably.
Moreover, the conventional method of manufacturing the commutator has been such that it is made of a metal material alone, and the brush to be contacted with the commutator is made of carbon. In practical use of these commutator and brush, since the metal material constituting the commutator and carbon constituting the brush have different material hardness from each other, and, moreover, since the circumference of the commutator to be in contact with the brush is longer than the length of contact of the brush with the commutator, the brush inevitably suffers from serious wear and tear for the difference in the material hardness and the contact length with the consequence that not only much time is taken for replacing the brush, but also brush replacement per se is uneconomical, if not impossible, hence the service life of the motor, etc. is naturally limited.